Question 18
Let $f(x)=\sqrt{x^2-10x+314}+\sqrt{x^2+20x+325}$. Find the minimum value of $[f(x)]$ for real number $x$.
Source notation: $[t]$ denotes the greatest integer less than or equal to $t$.
Source notation: $[t]$ denotes the greatest integer less than or equal to $t$.